In a wireless communication system, a radio access network (RAN) usually comprises at least one mobile switching center (MSC), base station controller (BSC), and base transceiver system (BTS). Each BTS may radiate to define wireless coverage areas that serve wireless communication devices (WCDs) such as cell phones.
The air interface between a BTS and a WCD comprises one or more traffic channels that may support circuit-switched or packet-switched communication, or bearer traffic, between these devices. The needs of different types of applications may be best served by different types of traffic channels. For example, a voice over Internet Protocol (VoIP) application may require a low-latency traffic channel, while a web application may perform well on a best-effort traffic channel.
When idle, a WCD typically relinquishes some or all of its traffic channels, so that the RAN can allocate these channels to other WCDs. However, even a WCD that is not idle may not be allocated an appropriate type of traffic channel for a particular application. For example, suppose that a WCD is allocated one or more best-effort traffic channels for web browsing. If the WCD then originates or receives a voice call, the RAN will still have to allocate, for the WCD, at least one low-latency traffic channel to appropriately support the voice call. Thus, regardless of whether a WCD is idle or active, the RAN may need to allocate a traffic channel when the WCD becomes involved in a new communication session.
The type of traffic channel that the RAN allocates for given communication session is usually governed by a service option transmitted to the RAN by the WCD as part of communication session establishment. Service options may take the form of an integer that characterizes, among other things, the quality-of-service (QOS) requirements of a traffic channel.
The speed at which the RAN can allocate traffic channels for a WCD is a key performance metric of wireless services. For latency-sensitive applications, such as real-time voice, video, gaming, or various types of multi-media and media streaming applications, reducing the latency of communication session establishment even by just a few tens of milliseconds can have a noticeable, and positive, impact on user experience. Often, allocation of a traffic channel requires a RAN component to execute a channel allocation routine and to communicate information about the allocated channel to the WCD. The latter step may require transmitting one or more messages to, and receiving one or more messages from, the WCD.
As real-time applications become more prevalent in wireless communication systems, an operator of such a system may need to offer services with a QOS as good as, or better than, its competitors in order to grow both its subscriber base and its revenue. Thus, it is advantageous for an operator of a wireless communication system to take every reasonable opportunity to decrease the latency involved in communication session establishment.